1. Field of the Invention
The present invention relates to an electronic control apparatus for an internal combustion engine wherein an atmospheric pressure related value such as an atmospheric pressure is obtained through an arithmetic operation by using another control parameter for the internal combustion engine, and the thus obtained value is used as an auxiliary parameter for controlling.
2. Discussion of Background
As an electronic control apparatus for an internal combustion engine of this kind, there has been known publication such as Japanese Unexamined Patent Publication No. 159447/1989. The detail of the electronic control apparatus disclosed in the publication will be described with reference to FIG. 1 which is also used for the explanation of an embodiment of the present invention.
In FIG. 1, reference numeral 1 designates an internal combustion engine having a plurality of cylinders 2 mounted on an automobile in which only one cylinder 2 is illustrated, numeral 3 designates an intake valve for the internal combustion engine 1, actuated by a cam (not shown), numeral 4 designates an intake manifold of the internal combustion engine 1, numeral 5 designates an injector disposed for each of the cylinders, disposed in the intake manifold 4, and numeral 6 designates a surge tank connected at the upstream side of the intake manifold 4.
Numeral 7 designates a throttle valve disposed in an intake passage at the upstream side of the surge tank 6 to control the flow rate of air sucked into the internal combustion engine 1, numeral 8 designates a throttle sensor for detecting degrees of opening of the throttle valve 7, numeral 9 designates a by-pass passage connected between the upstream side and the downstream side of the throttle valve 7, numeral 10 designates a by-pass air quantity regulator, numeral 11 designates a hot wire type air flow sensor (AFS) as an air flow rate sensor which is disposed at the upstream side of the throttle valve 7 to detect the flow rate of air sucked into the internal combustion engine 1 by using a temperature dependence resistor, numeral 12 designates an air temperature sensor for detecting the temperature of air before it has been passed through the AFS 11, and numeral 13 designates an air cleaner disposed at an inlet port at the upstream side of the AFS 11 and the air temperature sensor 12.
Numeral 14 designates a water temperature sensor disposed in a cooling passage for the internal combustion engine 1 to detect the temperature of cooling water, numeral 15 designates an O.sub.2 sensor as an air-fuel ratio sensor attached to an exhaust pipe to detect the air-fuel ratio, numeral 16 designates a crank angle sensor for detecting a crank angle of the internal combustion engine, and numeral 17 designates an electronic control unit (ECU) which determines a fuel injection quantity on the basis of output signals supplied mainly from the AFS 11, the water temperature sensor 14 and the crank angle sensor 16, and controls the injector 5 for fuel injection in synchronism with the output signal of the crank angle sensor 16.
Also the output signals of the throttle sensor 8, the air temperature sensor 12 and the O.sub.2 sensor 15 are used as auxiliary parameters for the ECU 17. The ECU 17 performs also control for the by-pass air quantity regulator 10 so as to adjust the revolution number of the internal combustion engine 1, however, the detail of the operation is omitted.
FIG. 2 shows the internal structure of the ECU 17 shown in FIG. 1. In FIG. 2, reference numeral 171 designates a digital interface for receiving digital signals from the crank angle sensor 16, wherein the output of the digital interface is inputted to a port or an interruption terminal of the CPU 172. The CPU 172 is a well known microprocessor including an ROM 1721 in which the control programs of flows shown in FIGS. 4 and 5 and data related thereto are written, an RAM 1722 as a work memory and a timer 1723. The CPU 172 generates a value such as a fuel injection pulse width calculated in accordance with a predetermined control program through an output of the timer.
Reference numeral 173 designates an analog interface for receiving analog signals from steady operation detecting means such as the throttle sensor 8, the AFS 11, the air temperature sensor 12, the water temperature sensor 14 and the O.sub.2 sensor 15. The outputs of the analog interface 173 are sequentially selected by a multiplexer 174 and is subjected to analog-digital conversion by an A/D converter 175 so that digital values are supplied to the CPU 172.
Numeral 176 designates a first driving circuit which drives the injector 5 with a fuel injection pulse width operated by the CPU 172. Numeral 177 designates a second driving circuit which drives the by-pass air quantity regulator 10 with an ISC driving pulse width which is calculated in accordance with a predetermined control program and generated through an output terminal of the timer.
The CPU 172 stores as a two-dimensional map the charging efficiency .eta..sub.co under a reference atmospheric condition of an atmospheric pressure of P.sub.o and an air temperature T.sub.o wherein the revolution number and the throttle opening degree are used as parameters. Further, the CPU 172 previously stores set data for judging and calculating. In addition, the CPU 172 stores in a form of map the maximum air flow rate value Q.sub.maxo under the reference atmospheric condition in the ROM 1721 wherein the revolution number is used as a parameter, for instance.
The operation of the CPU 172 will be described. First of all, an atmospheric correction value is obtained by using the following formula 1 wherein P.sub.a is an atmospheric pressure value used for controlling the operation characteristic quantity of the internal combustion engine, the value being outputted from the AFS for instance, P.sub.o is a set atmospheric value under a reference atmospheric condition, T.sub.a is an air temperature value detected by and outputted form the air temperature sensor 12, T.sub.o is a reference air temperature set value under a reference air condition, .eta..sub.c is a charging efficiency and .eta..sub.co is a charging efficiency under the reference atmospheric condition: ##EQU1##
Explanation of the theoretical ground of the formula 1 is omitted.
The operation of obtaining the atmospheric pressure correction value with use of the formula 1 will be described with reference to FIG. 4.
At Step S0, a charging efficiency .eta..sub.c at present is obtained by the calculation of the following formula 2 by using a revolution number signal N detected by the crank angle sensor 16, an air flow rate value Q.sub.a from the AFS 11 (or an air flow rate value Q.sub.a detected by the AFS 11 in FIG. 5), a predetermined cylinder capacity V.sub.H and an air density .rho..sub.o (the cylinder capacity and the air density are previously memorized) under a reference atmospheric condition: ##EQU2##
At Step S1 and Step S2, determination is made as to whether or not the operational condition at present is a steady operation. Namely, Step S1 is a step for judging whether or not the absolute value .vertline..DELTA..theta..vertline. of a deviation of the throttle opening degree in every predetermined time which is obtained by a routine (not shown) is a predetermined value .theta..sub.T or higher. When it is found that the absolute value assumes the predetermined value or higher, a steady operation continuing counter is reset to 0 at Step S3 under the recognition that it is a transient operation. When the absolute value is lower than the predetermined value .theta..sub.T, determination is made as to whether or not the absolute value .vertline..DELTA.N.vertline. of a deviation of the revolution number in every predetermined time which is obtained by a routine (not shown) is a predetermined value N.sub.T or higher at Step S2.
When it is revealed to be the predetermined value or higher, the transient operation is conducted, and the steady operation continuing counter is reset to 0 at Step 3. When the value is lower than the predetermined value N.sub.T, a steady operation is continued, and the steady operation continuing counter is increased by "1" at Step S4. After the completion of Step S3 or Step S4, determination is made as to whether or not the steady operation continuing counter counts a predetermined time m or more at Step S5. When the counter shows the predetermined time m or more, the steady operation is considered to continue for the predetermined time m or more, and sequential operation is moved to Step S6. When the counter counts less than the predetermined time m, the treatment shown in FIG. 4 is finished.
At Step S6, a charging efficiency .eta..sub.co under the reference atmospheric condition is obtained by looking up a two-dimensional map including throttle opening degree and revolution number N which is prepared with signals of throttle opening degree detected by the throttle sensor 8 and signals of the revolution number N detected by the crank angle sensor 16.
Then, at Step S7, an atmospheric pressure correction value C.sub.p (=P.sub.a /P.sub.o) is obtained through calculation in accordance with the formula 1 wherein the air temperature set value T.sub.o, the charging efficiencies .eta..sub.co and .eta..sub.c obtained in accordance with the above-mentioned operations and an air temperature value T.sub.a detected by the air temperature sensor 12 are used.
At Step S8, filtering treatment of the atmospheric pressure correction value C.sub.p is conducted. The filtering treatment is conducted by operating the following formula: EQU C.sub.p (i)=K.multidot.C.sub.p (i-1)+(1-k).multidot.C.sub.p
wherein k is a value of from 0 to 1 and C.sub.p (i-1) is an atmospheric pressure correction value obtained by the previous treatment. The atmospheric pressure correction value C.sub.p or an atmospheric pressure correction value C.sub.p (i) at present which is obtained after the filtering treatment are stored even after the key switch has been turned off, and they are immediately used for atmospheric pressure correction when the key switch is again turned on.
FIG. 5 is a flow chart of a routine to obtain an air flow rate value Q.sub.a by using the atmospheric pressure correction value.
At Step S21, the maximum air flow rate value Q.sub.maxo corresponding to each revolution number under the reference atmospheric condition is obtained. A symbol f.sub.(N) expresses a table of the maximum air flow rate value Q.sub.maxo using the revolution number as a factor. The maximum air flow rate value Q.sub.maxo is obtainable from the revolution number N obtained on the basis of the output signals of the crank angle sensor 16.
Step S22 is a step to determine a reverse flow region in the internal combustion engine 1 by using the revolution number N. Namely, when the revolution number N is in a range from N1 to N2 (i.e. N1&lt;N&lt;N2) i.e. in the reverse flow region and the sequential operation is moved to S23. Otherwise, sequential operation is moved to Step S24.
At Step S23, the maximum air flow rate Q.sub.maxo under the reference atmospheric condition is subjected to atmospheric pressure correction and temperature correction, and the maximum air flow rate value Q.sub.max at the current atmospheric condition is obtained by calculating the following formula 3: ##EQU3## where T.sub.o is an air temperature set value under the reference atmospheric condition and T.sub.a is an air temperature value at present detected by the air temperature sensor 12.
The term of temperature correction at the third term of the right side of the formula can be omitted for simplification of the system or it can be replaced by water temperature correction by the water temperature sensor.
At Step S24, the maximum air flow rate value Q.sub.maxo under the reference atmospheric condition is substituted for Q.sub.max. This step is conducted on the assumption of using the AFS capable of correctly measuring the air flow rate except for the reverse flow region. If such AFS is not used, the treatments of Step S22 and Step S24 are not conducted. It is also possible to omit the Step S22 and the Step S24 even when the AFS capable of correctly measuring the air flow rate.
Step S23 or Step S24 and Step S25 are steps for comparing an air flow rate value Q.sub.a measured by the AFS 11 with the maximum air flow rate value Q.sub.max. When Q.sub.a .gtoreq.Q.sub.max, the air flow rate value Q.sub.a is limited by Q.sub.max. When Q.sub.a &lt;Q.sub.max, no treatment is conducted and the series of treatments shown in FIG. 5 is finished.
In the conventional electronic control apparatus for an internal combustion engine having the construction as describe above, generally, there is a difference between response to a change of throttle opening degree in the throttle sensor and response to a change of air flow rate in the AFS. Further, there is a difference in delay time in processing analog signals in the analog interface and a timing of conversion in the A/D converter. Accordingly, there is a case of lacking simultaneity between the air flow rate value Q.sub.a for obtaining the charging efficiency .eta..sub.c at present in the formula 1 and the throttle opening degree .theta. or the revolution number N for obtaining the charging efficiency .eta..sub.co under the reference atmospheric condition, just after having moved from the steady operation to a transient operation. Nevertheless, the atmospheric pressure correction value C.sub.p may be obtained on the basis of the formula 1 on the judgment that the steady operation continues yet. In such case, the atmospheric pressure correction value C.sub.p is deviated from a correct value. As a result, correction of, for instance, the maximum air flow rate value becomes incorrect, whereby the air fuel ratio at the full open operation of the engine becomes excessively thick or thin.